A new dinosaur found in South Africa has given scientists a glimpse into the evolution of sauropods, the biggest animals ever to have walked the Earth, a new study says. The newfound, 20-foot-long (7-meter-long) dinosaur species is a close cousin to the common ancestor of all sauropods -- gigantic, four-legged, long-necked, big-bellied plant-eaters. Dubbed Aardonyx celestae, the 195-million-year-old dinosaur had a lot of sauropod-like features, such as a robust skeleton for holding up its heft. (See extreme dinosaur pictures.) Unlike sauropods, though, the newfound species walked on two legs and only dropped down on all fours, the new research shows....